Several studies have reported an association between deviant behaviour and cortisol reactivity to stress. However relatively few studies have investigated the relationship between psychobiological stress reactivity and sexual risk taking behaviours. In the present study, cortisol reactivity to the Trier Social Stress Test (TSST) was measured in 26 healthy young adults prior to the administration of a sexual health and behaviour questionnaire. The cortisol response to the TSST was greater in those individuals who reported that at least one of their previous two sexual partners was someone whom they had just met. Results are discussed in context of a model which suggests that early life stress dysregulates the hypothalamic-pituitary-adrenal (HPA) axis and increases the likelihood of later life risk taking behaviour. The findings have implications in terms of improving our understanding of psychobiological factors which predispose individuals to engage in adverse sexual health behaviours.